"Steven P. McNicoll" wrote in message
ink.net...

"Tony Cox" wrote in message
link.net...

And isn't airspace above FL600 in the US class E?


Yes.



Why the need for a change at that altitude?


Well, above some level there's just no need for it to be Class A anymore.
The level decided upon was FL 600.

Yes, but surely an IFR flight plan would be just as valid when ascending
through FL600 as when descending below FL180.

Assuming the mode C is properly calibrated, that is.